The present invention is directed to a system and method to maximize capacity and/or range of a wireless radio communication link between two radio communication devices.
Multiple-input multiple-output (MIMO) radio communication techniques are known to enhance the received SNR for signals transmitted by one device to another. Research in MIMO radio algorithms has been conducted in which multiple signal streams are transmitted simultaneously from multiple antennas at one device to another device, thereby greatly enhancing the data rate of the wireless radio channel between two devices. Such multiple signal stream systems are also referred to as “vector” communication systems, where a vector comprises a plurality of sub-channels that corresponding to the multiple signal streams. Moreover, the term eigenmodes or mode is also used to refer to a sub-channel or signal stream.
The aforementioned U.S. application Ser. No. 10/627,537 discloses a system, method and device for vector transmit beamforming communication of multiple signals (signal streams) between a first device having N plurality of antennas and a second device having M plurality of antennas. Unlike prior approaches, the approach described in that commonly assigned and related application is to impose a power constraint on each transmit antenna path at the transmitting device. The performance of a system in which the communication devices are designed around a power constraint at each antenna is nearly as good as the optimal waterfilling solution, yet provides significant implementation advantages. The radio transmitter can be implemented with power amplifiers that require lower power output capability, and thus less silicon area. Consequently, there is lower DC current drain by the transmitter, and lower on-chip interference caused by the power amplifiers.
In vector radio communication systems that simultaneously transmit multiple signals (modes) between first and second devices using MIMO radio techniques, it is necessary to use appropriate values for transmit weights conditioned to the radio channel between the two devices. While techniques have been developed for this purpose, there is nevertheless room for improvement in this area.